Hank Lentfer grew up watching Southeast Alaska’s glaciers grow thin and retreat from the shore. “The ecology is shifting literally overnight from having glaciers in the water to not,” says the manager of The Nature Conservancy’s Gustavus Forelands Preserve on Glacier Bay. “The pace of change is apparent for anybody who has lived here.”
Unlike other spots on the globe where significant loss of glaciers is a relatively recent development, Glacier Bay’s ice sheets have been melting, rapidly, for at least 200 years. Western civilization’s first recorded glimpse of Glacier Bay occurred in 1794, when members of Captain George Vancouver’s expedition described a glacier thousands of feet thick where today’s narrow, 65-mile long waterway now sits. The bulk of that glacier melted during the 19th century, at the end of what is called the Little Ice Age. It was not really an ice age as much as a 500-year-long cold spell.
Now, as climate change ignites a new round of melting, geologists, chemists and ecologists are measuring the changes and speculating what will happen once Glacier Bay simply doesn’t have any of its namesake sheets of ice anymore.
One of the most striking changes is the land itself. It is literally rising up as the weight of the glaciers decreases. The rate at which it’s rising is faster than at any other place on Earth: 15 feet in the past 150 years. On the coast, that means shoreline areas like the Conservancy’s Gustavus Forelands Preserve are growing in size, as land rises and the ocean waters retreat. Because the legal boundary of the preserve is mean high tide, says Lentfer, the preserve is getting larger. A recent survey of the property revealed that it had gained an additional 1,100 acres of dry land—former underwater habitat—since it was surveyed in 1921.
Chris Larsen, a research professor at the University of Alaska’s Geophysical Institute, has tracked the region’s rising land with GPS markers and tide gauges, but says the phenomenon is most clearly seen in the trees.
Near the water, tangles of young spruces and alders grow on sand and shells. Further inland, the land typically rises steeply; and beyond the rise, one finds old-growth forest with deep soils. “It’s an abrupt change,” Larsen says. The rise marks the former shoreline, before the glacier melted. Lentfer sees this when he digs in his own yard deep in a spruce forest, finding sand and clamshells—a sign that not so long ago, the ocean reached that spot.
As glaciers disappear, the melting water creates streams and adds nutrients to the marine environment. That might seem like more habitat is being created for economically valuable species like salmon. Unfortunately, the new streams that appear between retreating glaciers and the ocean are not welcoming to most salmon species, says Gordon Reeves, a research fish ecologist with the U.S. Forest Service’s Pacific Northwest Research Station in Corvallis, Oregon. Young salmon that grow up in fresh water need pools to rest in, trees or other vegetation for cover, and, most important, bugs to eat, he says. Glacial streams are cold, swift and lacking in tree cover. They don’t harbor many insects for salmon to eat.
So far, Reeves says, it appears that pink salmon are the first to colonize new glacial streams. “They don’t have much dependence on fresh water,” he says. “They just need it as spawning habitat.” Chum salmon come next, he says. They are an adaptable salmon species that also doesn’t spend much time in fresh water.
Shaking Up the Cocktail
Although daunting to salmon, glacial streams provide a bonanza to the marine environment. As glaciers grind across the landscape, they crush rocks that are rich in minerals, particularly iron and phosphorus, says Eran Hood, a biogeochemist at University of Alaska Southeast. Glaciers also contain microbes that are rich in carbon, another nutrient.
When the glacial runoff containing these minerals and nutrients hits the marine ecosystem, it feeds phytoplankton and other creatures at the bottom of the food chain. These creatures feed fish, which feed birds and seals, and so on. Soon you have humpback whales breaching and eagles soaring, and cruise ship tourists crowding the railing with binoculars to take it all in—thanks, in part, to glacial run-off.
As the region shifts from a predominantly glaciated landscape to a forested and alpine one, the mix of nutrients and micro-nutrients reaching the sea will shift as well, says Hood. “Glacier Bay is this cocktail of water from the ocean, water from glaciers and water from forests,” says Hood. “If the nutrients are different, the food web will be different.”
Other things will change as well. Plunge-diving sea birds find abundant prey near the upwelling of fresh water that occurs when glaciers touch the ocean, and harbor seals use icebergs calved from glaciers to raise their pups. As glaciers continue to melt and recede, these habitats will be lost.
Ultimately, Southeast Alaska’s lands and waters will remain productive and wild, if different in character. But knowing that doesn’t stop Hank Lentfer from sometimes missing the glaciers of his youth. “I find myself telling my 12-year-old daughter how these glaciers used to be,” he says. “They have retreated from the ocean into a life of story. My daughter won’t get to make her own stories with these glaciers,” he says, “but she’s making different stories in Southeast Alaska that are just as vibrant.” — NCM